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异常：

下面定义了一个CandleShop类：

class CandleShop:
    name = "Here's a Hot Tip: Buy Drip Candles"

    def __init__(self, stock):
        self.stock = stock

    def buy(self, color):
        self.stock[color] = self.stock[color] - 1


candle_shop = CandleShop({'blue': 6, 'red': 2, 'green': 0})
candle_shop.buy('blue')

1）自定义一个异常类OutOfStack

2）请修改实例buy当购买蜡烛的量超出库存时会抛出OutOfStack异常

3）想办法在主程序中加一个代码会引起程序抛出OutOfStack

4）捕获该异常，并输出异常的具体信息。

class CandleShop:
    name = "Here's a Hot Tip: Buy Drip Candles"

    def __init__(self, stock):
        self.stock = stock

    def buy(self, color):
        self.stock[color] = self.stock[color] - 1


class OutOfStack(Exception):     # (1)自定义一个异常类OutOfStack
    pass


def new_buy(self, color):      # (2)动态修改实例buy当购买蜡烛的量超出库存时会抛出OutOfStack异常
        if self.stock[color] > 0:
            self.stock[color] = self.stock[color] - 1
        else:
            raise OutOfStack("购买蜡烛的量超出库存!")     # 产生异常


try:
    candle_shop = CandleShop({'blue': 6, 'red': 2, 'green': 0})
    CandleShop.buy = new_buy
    candle_shop.buy('blue')
    candle_shop.buy('green')      # (3)加一个代码会引起程序抛出OutOfStack
except OutOfStack as e:      # (4)捕获该异常
    print(e)  # 输出异常的具体信息
else:
    print("蜡烛还有库存！")

注释详细，就不多解释了！